Pro-Apoptotic Function Analysis of the Reaper Homologue IBM1 in Spodoptera frugiperda

As an important type of programmed cell death, apoptosis plays a critical role in lepidopteran insects in response to various internal and external stresses. It is controlled by a network of genes such as those encoding the inhibitor of apoptosis proteins. However, there are few studies on apoptosis-related genes in Spodoptera frugiperda. In this study, an orthologue to the Drosophila reaper gene, named Sf-IBM1, was identified from S. frugiperda, and a full-length sequence was obtained by reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends PCR (RACE-PCR). The expression pattern of Sf-IBM1 was determined in different developmental stages and various tissues. Apoptotic stimuli including azadirachtin, camptothecin, and ultraviolet radiation (UV) induced the expression of Sf-IBM1 at both transcript and protein levels. Overexpression of Sf-IBM1 induced apoptosis in Sf9 cells, and the Sf-IBM1 protein was localized in mitochondria. The apoptosis induced by Sf-IBM1 could be blocked by the caspase universal inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (Z-VAD-FMK) and Sf-IAP1. Our results provide valuable information that should contribute to a better understanding of the molecular events that lead to apoptosis in lepidopterans.